Braking control device and braking control method

Abstract

To provide a technique that ensures the recovery amount of regenerative electric power while restricting slippage of wheels.SOLUTION: A braking control device 10 includes: a derivation unit 26 that derives a slip ratio of a wheel, on the basis of detected wheel speed and vehicle speed; a brake processor 28 that determines braking amounts to be applied to a regenerative braking device and a friction braking device, on the basis of an accelerator operation amount and a braking operation amount; and a controller 30 that controls the regenerative braking device and the friction braking device, on the basis of the determined braking amounts. When the slip ratio increases to a predetermined threshold value or more while the accelerator operation amount is decreasing, the controller 30 executes target slip control for controlling torque of a motor of the regenerative braking device on the basis of a predetermined target slip ratio to adjust the slip ratio, and when the target slip control is executed to perform the braking operation, the friction braking device generates a braking amount corresponding to the braking operation amount.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to braking control using a friction braking device capable of applying frictional force to a wheel and a regenerative braking device including a motor.

Background Art

[0002] Patent Document 1 discloses a braking control device that, when slip exceeding a set value occurs in a driving wheel when a vehicle control means performs coast regenerative braking in a coasting state, the vehicle control means executes coast regenerative braking control for reducing the coast regenerative braking torque.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technique disclosed in Patent Document 1, when slip exceeding a set value occurs in a wheel, the amount of recovered regenerative power may decrease because the coast regenerative braking torque is reduced. On the other hand, an increase in wheel slip is not preferable.

[0005] An object of the present invention is to provide a technique for ensuring the amount of recovered regenerative power while suppressing wheel slip.

Means for Solving the Problems

[0006] In order to solve the above problems, an aspect of the present invention is a braking control device that controls a regenerative braking device provided for a regenerative braking wheel of either the front wheel or the rear wheel, and a friction braking device capable of individually controlling the frictional braking force applied to the front wheel and the rear wheel, the braking control device including: an acquisition unit that acquires a detection result of an accelerator operation amount of an accelerator pedal, a detection result of a brake operation amount of a brake pedal, a detection result of wheel speeds of the front wheel and the rear wheel, and a detection result of a vehicle speed; a derivation unit that derives a slip ratio of a wheel based on the detected wheel speeds and the vehicle speed; a braking processing unit that determines a braking amount to be applied to the regenerative braking device and the friction braking device based on the accelerator operation amount and the brake operation amount; and a control unit that controls the regenerative braking device and the friction braking device based on the determined braking amount. When the slip ratio becomes equal to or greater than a predetermined threshold value when the accelerator operation amount decreases, the control unit executes target slip control for adjusting the slip ratio by controlling the torque of the motor of the regenerative braking device based on a predetermined target slip ratio, and when the target slip control is executed and a brake operation is performed, the control unit causes the friction braking device to generate a braking amount corresponding to the brake operation amount.

[0007] Another aspect of the present invention is a braking control method. This method is a braking control method in which each step is executed by a braking control device that controls a regenerative braking device provided for either the front or rear regenerative braking wheel and a friction braking device capable of individually controlling the frictional braking force applied to the front and rear wheels, and includes a step of obtaining a detection result of the accelerator operation amount of the accelerator pedal, a detection result of the brake operation amount of the brake pedal, a detection result of the wheel speeds of the front and rear wheels, and a detection result of the vehicle speed; a step of deriving a slip ratio of the wheels based on the detected wheel speeds and vehicle speed; a step of determining a braking amount to be applied to the regenerative braking device and the friction braking device based on the accelerator operation amount and the brake operation amount; and a step of controlling the regenerative braking device and the friction braking device based on the determined braking amount. In the control step, when the slip ratio becomes equal to or greater than a predetermined threshold value when the accelerator operation amount decreases, target slip control is executed to control the torque of the motor of the regenerative braking device based on a predetermined target slip ratio to adjust the slip ratio, and when the target slip control is executed and the brake operation amount is executed, a braking amount corresponding to the brake operation amount is generated by the friction braking device.

Effect of the Invention

[0008] According to the present invention, it is possible to provide a technique for ensuring the amount of recovered regenerative power while suppressing wheel slip.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] FIG. 1 is a diagram showing the functional configuration of the braking system 1. Each function of the braking system 1 can be configured, in terms of hardware, by circuit blocks, memories, and other LSIs, and in terms of software, can be realized by system software, application programs, etc. loaded into the memory. Therefore, it is understood by those skilled in the art that each function of the braking system 1 can be realized in various forms by hardware only, software only, or a combination thereof, and is not limited to any one of them. The braking system 1 is provided in a vehicle, and the vehicle may be capable of autonomous driving.

[0011] The braking system 1 includes a braking control device 10, an accelerator pedal sensor 12, a brake pedal sensor 14, a vehicle speed sensor 16, a wheel speed sensor 18, a friction braking device 20, and a regenerative braking device 22.

[0012] The accelerator pedal sensor 12 detects the operation amount of the accelerator pedal and transmits the detection result to the braking control device 10. The brake pedal sensor 14 detects the operation amount of the brake pedal and transmits the detection result to the braking control device 10. The accelerator pedal sensor 12 and the brake pedal sensor 14 are, for example, stroke sensors that detect the depression amount of the pedal. Note that even if a sensor that detects the master cylinder pressure is used instead of the brake pedal sensor 14, the operation amount of the brake pedal can be detected.

[0013] The vehicle speed sensor 16 detects the vehicle speed and transmits the detection result to the braking control device 10. The wheel speed sensor 18 is provided for each wheel, detects the wheel speed of each wheel, and transmits the detection result to the braking control device 10. Another in-vehicle sensor used for braking control is provided in the vehicle. For example, a sensor that detects the deceleration of the vehicle, a sensor that detects the torque of the motor provided in the regenerative braking device 22, etc. are provided.

[0014] The friction braking device 20 is provided for each wheel and can individually control the friction braking forces applied to the front wheels and the rear wheels. The friction braking device 20 advances and retracts a piston by hydraulic pressure, and by pushing the brake pad toward the brake disk as the piston advances, a braking force is applied to the wheel.

[0015] The regenerative braking device 22 is provided for either the front or rear regenerative braking wheel. The regenerative braking wheel may be, for example, the rear wheel. The regenerative braking device 22 includes a motor, an inverter, and a battery. The motor can generate a driving torque for rotating the wheel and can apply a regenerative torque to the rotation of the regenerative braking wheel when the vehicle decelerates. The regenerative power generated by the regenerative torque of the motor is charged to the battery. The regenerative torque can be adjusted by the control of the inverter.

[0016] The braking control device 10 controls the friction braking device 20 and the regenerative braking device 22 based on the detection results of various in-vehicle sensors. The braking control device 10 includes an acquisition unit 24, a derivation unit 26, a braking processing unit 28, and a control unit 30.

[0017] The acquisition unit 24 acquires the detection result of the accelerator operation amount of the accelerator pedal, the detection result of the brake operation amount of the brake pedal, the detection result of the wheel speeds of the front and rear wheels, and the detection result of the vehicle speed. Further, the acquisition unit 24 acquires the detection results from sensors that detect the torque of the regenerative braking device 22 and sensors that detect the deceleration of the vehicle.

[0018] The derivation unit 26 derives the slip ratio of each wheel based on the detected wheel speeds and vehicle speed. The slip ratio of the wheel refers to the ratio of the difference between the vehicle speed and the wheel speed to the vehicle speed.

[0019] The braking processing unit 28 includes a braking amount calculation unit 32, a target slip processing unit 34, and an allocation unit 36. The braking amount calculation unit 32 determines the braking amount to be applied to the regenerative braking device 22 and the friction braking device 20 based on the accelerator operation amount and the brake operation amount. The braking amount calculation unit 32 may separately determine the braking amount corresponding to the accelerator operation amount and the braking amount corresponding to the brake operation amount. The braking amount may be torque or deceleration.

[0020] When the accelerator operation amount is decreasing, that is, during coasting, the braking amount calculation unit 32 determines the regenerative torque generated in the regenerative braking device 22 as the braking amount corresponding to the accelerator operation amount. When the accelerator operation amount is decreasing, the regenerative braking device 22 generates regenerative torque to obtain regenerative power.

[0021] The target slip processing unit 34 determines to execute target slip control. The target slip control is control for adjusting the slip ratio by controlling the torque of the motor of the regenerative braking device 22 based on a predetermined target slip ratio. The target slip processing unit 34 determines to execute the target slip control when the accelerator operation amount is decreasing, that is, when the slip ratio of the wheels becomes equal to or greater than a predetermined threshold during coasting. The case where the slip ratio of the wheels becomes equal to or greater than a predetermined threshold may be that the average value of the slip ratios of each wheel becomes equal to or greater than the predetermined threshold, or that the slip ratio of any one wheel becomes equal to or greater than the predetermined threshold. The predetermined threshold is set to a value smaller than the slip ratio at which the ABS (Anti-lock Brake System) starts to operate. For example, the slip ratio at which the ABS starts to operate is about 12%, and the target slip control is executed before the ABS starts to operate and is controlled to maintain a target slip ratio smaller than 12%. The control unit 30 controls the torque of the motor of the regenerative braking device 22 so that the slip ratio of the wheels maintains a predetermined target slip ratio. The target slip ratio may be a predetermined fixed value or may vary according to vehicle state quantities such as vehicle speed and yaw rate and driver operation quantities such as steering.

[0022] In target slip control, the control unit 30 can adjust the regenerative torque of the regenerative braking device 22 to allow the slip ratio of the wheels at a certain rate while obtaining regenerative power. Since the target slip control is executed when the slip ratio of the wheels is equal to or greater than a predetermined threshold value, it is executed in a situation where slip is likely to occur due to the influence of rain, snow, etc. By the target slip control, it becomes difficult to execute the ABS and the running is stabilized, and the regenerative power can be ensured. The target slip control ends when a series of braking controls ends. A series of braking controls refers to the period from when the accelerator pedal is released and the accelerator operation amount starts to decrease, to when the brake pedal is depressed and the brake operation amount increases, and finally to when the brake pedal is released and the brake operation amount becomes zero.

[0023] The braking amount calculation unit 32 calculates a braking amount corresponding to the brake operation amount. The allocation unit 36 allocates the braking amount to be executed by the friction braking device 20 and the regenerative braking device 22 with respect to the determined braking amount. When the running state and the running environment of the vehicle are in good condition, the regenerative braking device 22 is preferentially allocated over the friction braking device 20. In the control for preferentially allocating the regenerative braking device 22, the allocation unit 36 allocates the braking amount up to the maximum regeneration amount of the regenerative braking device 22, and compensates for the insufficient braking amount with the friction braking device 20. The control unit 30 controls the regenerative braking device 22 and the friction braking device 20 based on the braking amount determined by the braking processing unit 28.

[0024] When the target slip control is executed and the brake operation amount increases, the allocation unit 36 generates the braking amount corresponding to the brake operation amount only by the friction braking device 20. When this brake operation is turned on, the regenerative torque obtained in the target slip control may be maintained or decreased, but an increase in the regenerative torque is restricted. Thereby, the braking control can be stabilized. The operation when executing the target slip control will be described with reference to new drawings.

[0025] FIG. 2 is a diagram for explaining the braking control when the target slip control is executed. The horizontal axis in FIGS. 2(a) to 2(d) is time, and the time from the time t1 to the time t4 is the same time.

[0026] The vertical axis of Fig. 2(a) is speed, and the vehicle speed 40 and the wheel speed 42 are shown. The vertical axis of Fig. 2(b) is the operation amount, and the accelerator operation amount 44 and the brake operation amount 46 are shown. The vertical axis of Fig. 2(c) is the regenerative torque, and the accelerator regenerative torque 48 and the brake regenerative torque 50 are shown. The vertical axis of Fig. 2(d) is the friction amount, and the front wheel friction amount 52 and the rear wheel friction amount 54 are shown.

[0027] Fig. 2(b) shows that the accelerator operation amount 44 starts to decrease from time t1, and Fig. 2(c) shows that the accelerator regenerative torque 48 starts to increase from time t1. At this time, as shown in Fig. 2(d), the friction braking device 20 is not operating. Fig. 2(a) shows that the wheel speed 42 starts to deviate from the vehicle speed 40 from time t1, and the slip ratio becomes equal to or greater than a predetermined threshold value at time t2, and the target slip control is started.

[0028] Fig. 2(c) shows that the accelerator regenerative torque 48 increases and decreases within a certain range and shows a waveform due to the start of the target slip control between time t2 and time t3. Fig. 2(a) shows that the wheel speed 42 decreases along the target slip value 43 due to the start of the target slip control, and the difference from the vehicle speed 40 is kept constant. During the target slip control from time t2 to time t3, the friction braking device 20 is not executed. The coasting time from the accelerator to the brake is included between time t2 and time t3, and Fig. 2(b) shows that the brake operation amount 46 starts to increase from time t3.

[0029] In Fig. 2(d), as the braking operation amount 46 increases from time t3, the front wheel friction amount 52 and the rear wheel friction amount 54 increase. On the other hand, in Fig. 2(c), the accelerator regeneration torque 48 does not increase, and the brake regeneration torque 50 also does not increase. The accelerator regeneration torque 48 corresponds to the accelerator operation amount, and the brake regeneration torque 50 corresponds to the braking operation amount. From time t3, the accelerator regeneration torque 48 is constant, and the target slip control has ended. Thus, when the target slip control is executed, for subsequent braking operations, braking force is added only by the friction braking device 20. Thereby, the regeneration torque can be controlled to be continuous within a certain range from the target slip control, and in a situation where slip occurs, braking can be performed by the friction braking device 20 to suppress an increase in the slip ratio.

[0030] The front wheel friction amount 52 from time t3 is larger than the rear wheel friction amount 54, but the hydraulic pressure executed by the front wheel friction braking device 20 and the rear wheel friction braking device 20 is executed at an equal pressure. Thereby, the braking control can be simplified.

[0031] From time t3, the front wheel friction amount 52 and the rear wheel friction amount 54 start to increase simultaneously, but the control unit 30 may start increasing the front wheel friction amount 52 earlier than the rear wheel friction amount 54 and increase the rear wheel friction amount 54 with a slight delay. Note that the rear wheel is a regenerative braking wheel and the front wheel is a non-regenerative braking wheel.

[0032] When the regenerative braking wheel is not limited to the rear wheel, it is as follows. When the target slip control is executed and the braking operation amount is executed, the control unit 30 causes the friction braking device 20 corresponding to the non-regenerative braking wheel among the friction braking devices 20 corresponding to the front and rear wheels to generate a braking amount earlier than the friction braking device 20 corresponding to the regenerative braking wheel. Since the regenerative braking force is applied to the regenerative braking wheel by the regenerative braking device 22, by applying the braking force to the non-regenerative braking wheel earlier for the braking operation, the bias of the braking force between the front and rear wheels can be suppressed at the initial stage of the braking operation.

[0033] When the braking control device 10 attempts to obtain the maximum amount of regenerative torque under bad road surface conditions, the slip ratio increases, and there is a risk that the ABS will activate prematurely. From time t3, the difference between the wheel speed 42 and the vehicle speed 40 has increased slightly due to the braking operation, but since the regenerative torque has not increased, the increase in the slip ratio is suppressed.

[0034] Return to FIG. 1. When the brake operation amount increases after the target slip control is not executed when the accelerator operation amount decreases, the allocation unit 36 executes control to limit the braking amount generated by the regenerative braking device 22 when the absolute value of the difference in slip ratio between the front and rear wheels becomes equal to or greater than a predetermined value. Regarding the control of the situation where slipping occurs during the braking operation without executing this target slip control, an explanation will be given while referring to new drawings.

[0035] FIG. 3 is a diagram for explaining the braking control when the target slip control is not executed. The horizontal axis in FIGS. 3(a) to 3(d) is time, and the time from that time t1 to time tt is the same time.

[0036] The vertical axis in FIG. 3(a) is speed, and the vehicle speed 60 and the wheel speed 62 are shown. The vertical axis in FIG. 3(b) is the operation amount, and the accelerator operation amount 64 and the brake operation amount 66 are shown. The vertical axis in FIG. 3(c) is the regenerative torque, and the accelerator regenerative torque 68 and the brake regenerative torque 70 are shown. The vertical axis in FIG. 3(d) is the friction amount, and the front wheel friction amount 72 and the rear wheel friction amount 74 are shown.

[0037] In FIG. 3(b), it is shown that the accelerator operation amount 64 starts to decrease from time t1, and in FIG. 3(c), it is shown that the accelerator regenerative torque 68 starts to increase from time t1. At this time, as shown in FIG. 3(d), the friction braking device 20 is not operating. In FIG. 3(a), from time t1, the wheel speed 62 deviates slightly from the vehicle speed 60, but since the slip ratio is small, the target slip control is not executed.

[0038] At time t2, the accelerator operation turns off. In Fig. 3(c), the accelerator regeneration torque 68 increases between time t1 and time t2, and becomes a constant value after time t2. Between time t2 and time t3, it is the coasting time when switching from the accelerator to the brake, and a constant accelerator regeneration torque 68 is applied, while the vehicle speed 60 and the wheel speed 62 are decreasing.

[0039] From time t3, the brake operation amount 66 in Fig. 3(b) starts to increase, the brake regeneration torque 70 in Fig. 3(c) starts to increase, and the front wheel friction amount 72 and the rear wheel friction amount 74 in Fig. 3(d) do not increase. This is because the regenerative braking of the regenerative braking device 22 is executed preferentially over the friction braking device 20.

[0040] In Fig. 3(a), from time t3, the wheel speed 62 starts to deviate from the vehicle speed 60, and when the absolute value of the difference in the slip ratios of the front and rear wheels becomes equal to or greater than a predetermined value at time t4, the braking processing unit 28 determines to limit the braking amount generated by the regenerative braking device 22. Therefore, from time t4, the brake regeneration torque 70 starts to decrease, and the front wheel friction amount 72 starts to increase.

[0041] At time t5, the increase in the brake operation amount 66 stops, the decrease in the brake regeneration torque 70 stops, and the increase in the front wheel friction amount 72 stops. In Fig. 3(a), from time t4, the wheel speed 62 deviated from the vehicle speed 60 and the slip ratio increased, but by increasing the ratio of friction braking over regenerative braking, the slip ratio decreased and at time t5, the slip ratio is within the allowable value. Thus, when the target slip control is not executed, when the slip ratio increases due to the brake operation, the ratio of regenerative braking can be reduced to decrease the slip ratio.

[0042] The condition for restricting the regenerative braking at time t4 is determined by the absolute value of the difference in the slip ratios of the front and rear wheels, making it difficult to execute the restriction of the regenerative braking while enabling the start of the restriction of the regenerative braking at the timing when slip surely occurs. Note that the condition for restricting the regenerative braking at time t4 may be satisfied when the slip ratio of the wheel is equal to or greater than a predetermined threshold value. That is, when a predetermined condition indicating that the slip ratio of the wheel has become greater than or equal to the set value after the target slip control is not executed is satisfied, the braking processing unit 28 determines to limit the braking amount generated by the regenerative braking device 22.

[0043] From time t4, the braking processing unit 28 sets a limit value for the braking amount of the regenerative braking device 22, and the control unit 30 controls such that the brake regeneration torque 70 becomes equal to or less than the limit value. The limit value for the braking amount of the regenerative braking device 22 is set based on the slip ratio of the regenerative braking wheel. The slip ratio of the regenerative braking wheel may be the average value of the slip ratios of the left and right wheels, or may be the slip ratio of either one of the left and right wheels. As the slip ratio of the regenerative braking wheel increases, the limit value for the braking amount of the regenerative braking device 22 decreases, and when the slip ratio of the regenerative braking wheel becomes equal to or greater than a predetermined threshold value, the limit value of the regenerative braking device 22 becomes zero, and the brake regeneration torque 70 is restricted to become zero.

[0044] Note that as shown in FIG. 3(c), even when the brake regeneration torque 70 is restricted from time t4, the accelerator regeneration torque 68 remains at a constant value. Thereby, a sudden change in the regeneration torque can be suppressed. When the brake regeneration torque 70 is restricted, the accelerator regeneration torque 68 may also be gradually decreased. Here, the amount by which the accelerator regeneration torque 68 is decreased does not have to be compensated by the friction braking device 20.

[0045] At time t4, the limitation of the braking amount of the regenerative braking device 22 starts. However, if the increase in the slip ratio from time t3 is rapid, the operation of the ABS may not be suppressed by the limitation of the braking amount of the regenerative braking device 22. Therefore, in the braking operation after the target slip control is not executed, the braking processing unit 28 limits the increase amount per unit time of the brake regeneration torque 70 according to the acceleration rate of the brake operation amount 66 and the slip ratio.

[0046] Return to FIG. 1. The braking amount calculation unit 32 distributes the braking amounts of the front wheels and the rear wheels according to a preset distribution ratio. The allocation unit 36 allocates the braking amount distributed to the regenerative braking wheels to the friction braking device 20 and the regenerative braking device 22.

[0047] The braking control device 10 can stabilize braking by distributing more braking force to the front wheels than to the rear wheels. When the rear wheels are regenerative braking wheels, the accelerator regeneration torque is applied to the rear wheels first, and further braking force by the braking operation is applied to the rear wheels. Therefore, at the initial stage of braking, the braking force of the rear wheels becomes larger than the braking force of the front wheels, and there is a possibility that the slip ratio of the rear wheels increases depending on the driving state and driving environment of the vehicle. Therefore, the braking processing unit 28 varies the braking amount distribution between the front wheels and the rear wheels at the initial stage of braking by the braking operation, and distributes more braking force to the front wheels than to the rear wheels. This process will be described with reference to new drawings.

[0048] FIG. 4 is a diagram showing the relationship between the front wheel deceleration and the rear wheel deceleration when the regenerative braking wheels are the rear wheels. The vertical axis of FIG. 4 indicates the rear wheel deceleration, and the horizontal axis indicates the front wheel deceleration. When the braking control device 10 applies braking force, it is desirable to be close to the ideal distribution line 80 or the isobaric braking distribution line 82. The ideal distribution line 80 indicates the ideal distribution of deceleration, and the isobaric braking distribution line 82 indicates the distribution when the friction braking devices 20 of the front wheels and the rear wheels are controlled at the same pressure respectively.

[0049] When the regenerative braking wheels shown in FIG. 4 are the rear wheels, in the deceleration distribution transition 84 of the comparative example, the deceleration of the rear wheels increases due to the accelerator regeneration torque, and shifts to approach the ideal distribution line 80 when the braking operation is started.

[0050] In the braking force distribution transition 86 of the embodiment, when the deceleration of the rear wheels increases due to the accelerator regeneration torque and the braking operation is started, braking forces are applied to the front wheels and the rear wheels. At this time, when the braking operation amount, the accelerator regeneration torque, and the deceleration of the vehicle satisfy a predetermined condition, the braking processing unit 28 sets the deceleration of the rear wheels to a predetermined deceleration and compensates for the shortage with the front wheels. The control unit 30 gradually reduces the deceleration of the rear wheels so that it becomes the predetermined deceleration, and when the predetermined deceleration is reached, the gradual reduction is stopped and the deceleration of the rear wheels is maintained. The predetermined condition is satisfied if the braking operation amount and the accelerator regeneration torque are equal to or greater than a predetermined torque, the deceleration of the vehicle is equal to or greater than a predetermined torque, and the brake regeneration torque is equal to or greater than a predetermined value, and is satisfied, for example, when the vehicle is traveling on a highway. In this way, when the braking operation amount is large and a large deceleration is applied to the vehicle, the deceleration of the rear wheels can be decreased.

[0051] FIG. 5 is a flowchart of the braking control method of the embodiment. The acquisition unit 24 acquires the detection results of the accelerator pedal sensor 12 and the brake pedal sensor 14 and acquires the driver's pedal operation amount (S10). The braking processing unit 28 determines whether there is no braking operation (S12).

[0052] If there is no braking operation (Y in S12), the braking processing unit 28 determines whether the accelerator operation amount is decreasing (S14). If there is no braking operation and the accelerator operation amount is not decreasing (N in S14), this process ends without braking.

[0053] If the accelerator operation amount is decreasing (Y in S14), the derivation unit 26 derives the slip ratio of the wheels based on the vehicle speed and the wheel speed (S16). The braking processing unit 28 determines whether the slip ratio of the wheels is equal to or greater than a predetermined threshold (S18). If the slip ratio of the wheels is equal to or greater than the predetermined threshold (Y in S18), the target slip control is started and the adjusted accelerator regeneration torque is applied (S20).

[0054] If the slip ratio of the wheel is not equal to or greater than a predetermined threshold value (N in S18), a constant acceleration regeneration torque is applied by the regeneration braking device 22 (S22), and the vehicle runs in a so-called coast state.

[0055] If there is a braking operation (N in S12), the braking processing unit 28 determines whether target slip control is being executed in a series of braking controls (S24). When target slip control is being executed in a series of braking controls (Y in S24), braking in response to the braking operation is executed only by the friction braking device 20 (S26).

[0056] When target slip control is not being executed in a series of braking controls (N in S24), the derivation unit 26 calculates the slip ratio of the wheel (S28). The braking processing unit 28 determines whether the slip ratio of the wheel satisfies a predetermined condition (S30). The predetermined condition may be satisfied if the absolute value of the difference between the slip ratios of the front and rear wheels is equal to or greater than a predetermined value, or may be satisfied if the slip ratio of the wheel is equal to or greater than a predetermined threshold value.

[0057] When the slip ratio of the wheel satisfies the predetermined condition (Y in S30), the braking processing unit 28 determines to limit the braking amount of the regeneration braking device 22, and the control unit 30 controls the braking amount of the regeneration braking device 22 to be equal to or less than the limit value (S32).

[0058] When the slip ratio of the wheel does not satisfy the predetermined condition (N in S30), that is, when there is little slip in the wheel, the braking processing unit 28 preferentially allocates the regeneration braking device 22, and controls so that if the maximum braking amount of the regeneration braking device 22 is exceeded, the shortage is compensated by the friction braking device 20 (S34).

[0059] As described above, the present disclosure has been described based on the embodiments. The present disclosure is not limited to the above-described embodiments, and various design changes and other modifications can be made based on the knowledge of those skilled in the art.

Explanation of Reference Numerals

[0060] 1 Brake system, 10 Brake control device, 12 Accelerator pedal sensor, 14 Brake pedal sensor, 16 Vehicle speed sensor, 18 Wheel speed sensor, 20 Friction braking device, 22 Regenerative braking device, 24 Acquisition unit, 26 Derivation unit, 28 Brake processing unit, 30 Control unit, 32 Braking amount calculation unit, 34 Target slip processing unit, 36 Allocation unit.

Claims

1. A braking control device that controls a regenerative braking device provided for a regenerative braking wheel of either the front wheel or the rear wheel, and a friction braking device capable of individually controlling the frictional braking force applied to the front wheel and the rear wheel, comprising an acquisition unit that acquires a detection result of an accelerator operation amount of an accelerator pedal, a detection result of a brake operation amount of a brake pedal, a detection result of wheel speeds of the front wheel and the rear wheel, and a detection result of a vehicle speed; a derivation unit that derives a slip ratio of a wheel based on the detected wheel speed and vehicle speed; a braking processing unit that determines a braking amount to be applied to the regenerative braking device and the friction braking device based on the accelerator operation amount and the brake operation amount; and a control unit that controls the regenerative braking device and the friction braking device based on the determined braking amount. When the slip ratio becomes equal to or greater than a predetermined threshold value when the accelerator operation amount decreases, the control unit executes target slip control for adjusting the slip ratio by controlling the torque of the motor of the regenerative braking device based on a predetermined target slip ratio. When the target slip control is executed and a brake operation is executed, the friction braking device generates a braking amount corresponding to the brake operation amount. A braking control device characterized by this.

2. The braking processing unit, when a brake operation is executed after the target slip control is not executed when the accelerator operation amount decreases, causes the regenerative braking device to be executed preferentially over the friction braking device with respect to the braking amount corresponding to the brake operation amount, When a brake operation is executed after the target slip control is not executed when the accelerator operation amount decreases, and when the slip ratio satisfies a predetermined condition, executes control for limiting the braking amount generated by the regenerative braking device. The braking control device according to claim 1, characterized by this.

3. When the target slip control is executed and the braking operation amount is executed, the control unit causes the friction braking device that does not correspond to the regenerative braking wheel among the friction braking devices corresponding to the front wheels and the rear wheels to generate a braking amount earlier than the friction braking device corresponding to the regenerative braking wheel. The braking control device according to claim 1 or 2, characterized in that.

4. In the control for limiting the braking amount generated by the regenerative braking device, the braking processing unit sets a value for limiting the braking amount based on the slip ratio of the regenerative braking wheel. The braking control device according to claim 2, characterized in that.

5. A braking control method in which each step is executed by a braking control device that controls a regenerative braking device provided for a regenerative braking wheel of either the front wheels or the rear wheels and a friction braking device capable of individually controlling the frictional braking force applied to the front wheels and the rear wheels, Obtaining a detection result of the accelerator operation amount of the accelerator pedal, a detection result of the brake operation amount of the brake pedal, a detection result of the wheel speeds of the front wheels and the rear wheels, and a detection result of the vehicle speed; Deriving the slip ratio of the wheel based on the detected wheel speed and vehicle speed; Determining the braking amount applied to the regenerative braking device and the friction braking device based on the accelerator operation amount and the brake operation amount; Controlling the regenerative braking device and the friction braking device based on the determined braking amount, including In the step of controlling, when the slip ratio becomes equal to or greater than a predetermined threshold value when the accelerator operation amount decreases, target slip control is executed to control the torque of the motor of the regenerative braking device based on a predetermined target slip ratio to adjust the slip ratio. When the target slip control is executed and the brake operation amount is executed, a braking amount corresponding to the brake operation amount is generated by the friction braking device. The braking control method is characterized in that.

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